Geographic Information Systems
Coordinate Systems
1. Map Scale
►
A ratio between a distance on the map and the
corresponding distance on the earth
The distance on the map is always expressed as one, e.g.,
1 : 100,000
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Common map scales
1 : 24,000
1: 100,000
1 : 250,000
1 : 1,000,000
Map Scale
►
►
Small and large scale
Which one is a larger map scale?
1 : 24,000 or 1 : 100,000
Spatial scales
 Map scale (large vs. small)
 Resolution (fine vs. coarse)
 Extent (large vs. small)
2. Coordinate Systems
Basic elements of a coordinate system
► an origin, then the
location of every
other point can be
stated in terms of
► a defined direction and
► a distance in the
direction
2. Coordinate Systems
►
Spherical coordinate systems
Geographic coordinate system
► Rectangular coordinate systems
UTM (Universal Transverse Mercator)
State Plane
2 (1) Spherical Coordinate Systems
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►
Based on a perfect sphere
Geographic coordinate system
- great circles
small circles
- meridians
parallels
- Latitude
- Longitude
courtesy: http://www.colorado.edu/geography/gcraft/
Latitude
►
►
Measured northward or southward from the equator to
poles
Ranging 0-900 north or south
►
The measuring units are degrees, minutes, and seconds,
10 = 60’ and 1’=60”
►
The length of one degree latitude is similar everywhere, ≈
111km/69miles
Longitude
►
Measured eastward or westward from the Prime Meridian
at Greenwich, England to the International Date Line
►
Ranging 0-1800 east or west
►
The measuring units
►
Length of one degree longitude reduces toward poles
Latitude and Longitude
Lines of Latitude
900 latitude
(East/West - parallels)
Prime
Meridian 00
Lines of Longitude
(North/South - meridians)
courtesy: Mary Ruvane, http://ils.unc.edu/
Central Parallel 00
Reading Latitude and Longitude
►
►
19050’ S: 19 degrees 50 minutes Latitude South
43050’ W: 43 degrees 50 minutes Longitude West
- 43050’ W
2 (2) Rectangular Coordinate Systems
►
Also referred to as Planar, Cartesian, and Grid coordinate
system
►
It converts Earth’s curved surface onto a flat map surface
►
The x value is given first and called easting, then the y
value is given and called northing
2 (2) (i) UTM
►
Universal Transverse Mercator
coordinate system
►
A rectangular coordinate
system for the WORLD
Gerardus Mercator (1512-1594)
Courtesy of the Library of Congress, Rare Book Division, Lessing J. Rosenwald Collection.
UTM Zones and Rows
►
Measuring unit: meter
►
Map projection: Universal Transverse Mercator
►
Zones: north-south columns of 60 longitude wide, labeled
1 to 60 eastward beginning at the 1800 meridian
►
Rows: east-west rows of 80 latitude high, labeled from C
to X (without I, O) beginning at 800 S latitude
►
Quadrilaterals
UTM Zones of the World
courtesy: http://www.colorado.edu/geography/gcraft/
A UTM Zone
►
We always use zones
and rarely use rows
courtesy: http://www.colorado.edu/geography/gcraft/
UTM Easting and Northing
►
Each of the 60 zones has its own central meridian
►
The central meridian of a zone is given the easting of
500,000m and the equator is given a northing value of 0
for the northern hemisphere
►
For southern hemisphere, the equator is given a northing
value of 10,000,000m
►
671,000m Easting, 4,749,000m Northing
Calculate Your Own Zone
44003’ Latitude N, 71058’ Longitude W = Zone ?
courtesy: http://www.colorado.edu/geography/gcraft/
2 (2) (ii) State Plane Coordinate
►
A rectangular coordinate system for the UNITED STATES
►
Measuring unit: foot
►
Zones: The U.S. is divided into 120 zones. Zone boundaries
follow state and county lines
State Plane
http://www.cnr.colostate.edu/class_info/nr502/lg3/datums_coordinates/spcs.html
2 (2) (ii) State Plane Coordinate
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Projections: Each zone has its own projection system
- Transverse Mercator for states of N-S extent
- Lambert's conformal conic projection for states of E-W
extent
State Plane
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The central meridian of a zone is given 2,000,000ft False
Easting
►
False origin: it is established in the south and west of the
zone as 0, 0
►
False easting, and false northing
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Zones may overlap
Difference between Systems
UTM and many other coordinate systems are defined based
on the geographic coordinate system
Difference between Systems
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Try to use the rectangular systems as much as possible,
and not to use geographic system for calculation
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Remotely sensed imagery and digital elevation models
routinely use UTM
►
Land record system routinely use State Plane
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know how to convert between projections (will be
discussed in the lab)
3. Datum
►
Vertical datum: is the zero surface from which all
elevations or heights are measured
Datum
►
Geodetic datum: are established to provide positional
control that supports surveying and mapping projects
covering large geographic areas, such as a country, a
continent, or the whole world
North American Datum of 1927 (NAD27)
North American Datum of 1983 (NAD83)
►
Coordinates change if datum changes: a control point in
CA
On NAD83: -117 12 57.75961, 34 01 43.77884
On NAD27: -117 12 54.61539, 34 01 43.72995
4. Map Projections
►
►
A means of converting coordinates on a curved surface to
coordinates on a plane
Map projections vs. coordinate systems
- Map projections define how positions on the earth’s
curved surface are transformed onto a flat map surface
- Coordinate systems superimposed on the surface to
provide a referencing framework on which positions are
measured
Map Projections
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A classification of map projections
►
By conceptual methods
Cylindrical, Azimuthal, and Conic
►
By distortions
Conformal, Equal-area, Equidistant, and Azimuthal
Map Projections – by Methods
►
Cylindrical
1. Mercator
http://exchange.manifold.net
2. Transverse Mercator
Map Projections - by Methods
►
Azimuthal
►
Conic
http://exchange.manifold.net
Map Projections - by Distortions
►
Conformal projections
It retains shapes about a point
►
Equal-area projections
It retains correct relative size
►
►
Equidistant projections
It retains uniform scale in all directions but only from one
or two points
Azimuthal projections
It retains correct directions from one or two points
Map Projections - by Distortions
Conformal –
preserves shape
Equivalent -
preserves area
Equivalent preserves area
Compromise preserves neither
courtesy: Mary Ruvane, http://ils.unc.edu/
Commonly Used Projections
►
►
Transverse Mercator: cylindrical conformal
Lambert's conformal conic
http://www.youtube.com/watch?v=b1xXTi1nFCo&feature=
player_embedded
http://www.youtube.com/watch?v=AI36MWAH54s
Commonly Used Projections
►
►
UTM as a coordinate system
TM as a means of projection
Readings
►
Chapter 2
3. Topographic Maps
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Planimetric maps
- Graphical representation of the shape and horizontal
location of physical features of land and other physical
entities.
►
Topographic maps
- identity elevation of the land in contour lines.
Topographic Maps
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A map series published by USGS
►
It is bound by parallels on the north and south, meridians
on the east and west, 7.5’ span in either direction
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The maps are created from aerial photos
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The features are topography, vegetation, railroad, streams,
roads, urban, etc.
►
Three coordinate systems are marked, geographical, UTM,
and State Plane